Device for supporting a fuel pin cluster within a nuclear reactor fuel assembly wrapper

Abstract

A supporting member for an array of parallel rails each carrying one row of slidably mounted pins of a fuel cluster is placed coaxially at the lower end of a vertical fuel assembly wrapper. Each parallel rail is provided at each end with a downward extension and terminal lug which engages in a lateral groove formed in the periphery of the supporting member in order to lock and maintain the rails and the fuel pins in uniformly spaced relation within the fuel assembly wrapper.

What we claim is: 
     
       1. A device for supporting a cluster of fuel pins having end caps within the wrapper of a nuclear reactor fuel assembly comprising a coaxial supporting member at the lower end of the vertically-disposed fuel assembly wrapper, a plurality of parallel rails, grooves formed in the lower end-caps of a row of pins of the fuel cluster slidably engaged on the upper extremities of said rails, a lateral groove in and opening towards the periphery of said supporting member, fastening lugs forming lateral extensions of said rails, a re-entrant portion for each of said lugs mounted in said groove, said two fastening lugs for each of said rails being disposed in the plane of said rails, said re-entrant portions of said lugs for each of said rails engaging in two regions of said groove located on each side of a plane of symmetry at right angles to the plane of said rail and passing through the axis of the fuel assembly wrapper, locking means fixing the spacing between said parallel rails and extending into said groove within a space separating adjacent ones of said re-entrant portions of two adjacent rails. 
     
     
       2. A supporting device according to claim 1, said locking means including combs within said groove beneath said fastening lugs of the rails and teeth for said combs engaged between said lugs. 
     
     
       3. A supporting device according to claim 1, said locking means including blocks secured to one face of a rail. 
     
     
       4. A supporting device according to claim 1, including means for spacing said parallel rails directly attached to the pins of the cluster and providing constant spacing between a row of pins carried by one rail and a row of pins carried by one of the adjacent parallel rails. 
     
     
       5. A device for supporting a cluster of fuel pins having end caps within the wrapper of a nuclear reactor fuel assembly comprising a coaxial supporting member at the lower end of the vertically-disposed fuel assembly wrapper, a plurality of parallel rails, grooves formed in the lower end-caps of a row of pins of the fuel cluster slidably engaged on the upper extremities of said rails, a lateral groove in and opening towards the periphery of said supporting member, fastening lugs forming lateral extensions of said rails, a re-entrant portion for each of said lugs mounted in said groove, said two fastening lugs for each of said rails being disposed in the plane of said rail, said re-entrant portions of said lugs for each of said rails engaging in two regions of said groove located on each side of a plane of symmetry at right angles to the plane of said rail and passing through the axis of the fuel assembly wrapper; and means for spacing said parallel rails directly attached to the pins of the cluster and providing constant spacing between a row of pins carried by one rail and a row of pins carried by one of the adjacent parallel rails. 
     
     
       6. A supporting device according to claim 5, said spacing means including wires each wound in a helix of constant pitch on an external surface of a fuel pin and secured at one end to and at the level of the lower end-cap of said pin, the point of initial attachment of the wire of each pin being displaced by 60° about the axis of said pin. 
     
     
       7. A supporting device according to claim 5, said spacing means including an overthickness of the lower end-cap of each of said pins so that the end-caps of one row of pins are in contact with the end-caps of the adjacent row of pins. 
     
     
       8. A supporting device according to claim 7, wherein the overthicknesses of the end-caps each have a cylindrical profile. 
     
     
       9. A supporting device according to claim 7 wherein the overthickness of the end-caps each have a prismatic profile. 
     
     
       10. A supporting device according to claim 1 said locking means including blocks adjacent one face of the rails and connected to the rails when the rails are in said groove.